Recent increase in the environmental consciousness leads strong desire for the development of a detergent with low environmental load. A detergent having higher concentration of a cleaning component than that of conventional detergent, or a concentrated detergent, appears as being very effective for decreasing its own size to reduce an amount of resin used for container, a transportation cost, and a waste after use, resulting in reduction of loads on the environment.
A common liquid detergent however has a problem of seriously detracted usability due to thickening or gelation when it contains an increased amount of a surfactant as a cleaning component (e.g., 40% by mass or more). This is because the surfactant at high concentration forms a highly viscous phase such as of liquid crystal and crystal in the detergent composition. To provide a composition having a decreased viscosity, there is a method of adding a large amount of solvent to such a detergent composition containing a surfactant at high concentration for reducing a viscosity. The method however has problems of increased risk of the presence of a flash point in the composition and of damaging materials such as a container and a laundry machine. In addition, since the solvent does not contribute as a cleaning component, addition of a large amount of the solvent is not desirable in terms of formulation cost. The composition having an increased concentration of a surfactant has further problems in solubility and stability such as tendency of solidification of the composition during storage at low temperature. There is also a known liquid detergent having softening effects by blending cationic surfactant in the detergent. The detergent composition however has more serious problems in solubility and stability when it contains anionic surfactant and cationic surfactant together.
JP-A2008-7705, JP-A2008-7706, and JP-A2008-7707 describe concentrated liquid detergent compositions containing a specific nonionic surfactant.
JP-A11-217585 and JP-A01-132691 describe softening liquid detergents containing quaternary ammonium salt.
JP-A08-157867 describes a concentrated liquid detergent composition containing nonionic surfactant produced by adding ethylene oxide and propylene oxide to higher alcohol and specific solvent. In the text and Examples of the patent, exemplified as a preferred nonionic surfactant is ethylene oxide/propylene oxide block adduct produced by adding ethylene oxide and then propylene oxide.
JP-A09-255989 and JP-A11-241094 describe liquid detergents having a good rinsing property and good softening effect, comprising nonionic surfactant produced by adding propylene oxide and ethylene oxide to higher alcohol, anionic surfactant and cationic surfactant.
JP-A11-315299 describes a liquid detergent having good detergency and softening effect, containing nonionic surfactant having alkyl or alkenyl group of 8 to 20 carbon atoms and a sequence of polyethyleneoxy-polypropyleneoxy-polyethyleneoxy group added to the alkyl or alkenyl group in this order, alkylbenezenesulfonate salt, and a specific cationic surfactant.